Many signal formats are used for broadcast of television signals. For example, the high definition TV (HDTV), which is a next generation format, the standard definition TV (SDTV) such as NTSC and D2 (digitized NTSC). Standard NTSC is an interlaced signal format, and another format that is in use is non-interlaced, or progressive scan NTSC, which is converted from the original interlaced format to non-interlaced format by digital technology. The same program sometimes may be broadcast in multiple formats. Therefore, it may be necessary to convert a program recorded in one format such as HDTV into another format such as SDTV.
Even though two television signals may be of the same format and from the same source, they may be shifted in phase and not synchronized because, for example, the lengths of the respective signal paths are different. In such a case, the GEN lock system may be used to synchronize the signals.
A conventional waveform monitor has at least one channel which receives a television signal at an input terminal and processes the signal to allow the waveform monitor to display the waveform of the signal. The channel is able to extract the horizontal and vertical sync signals of the television signal and employ one of the sync signals to generate triggers, which control display of the waveform of the television signal.
A waveform monitor that has a trigger circuit particularly for television signals measures characteristics between the television signals in the GEN lock system such as level of synchronization or phase difference. The trigger circuit generates a trigger signal pulse, for example in response to a specific signal element such as the horizontal or vertical sync pulse of the input television signal, to generate a sweep signal in the waveform monitor so as to display repeatedly the waveform of a desired portion of the television signal.
In the above case, one of the television signals may be provided to the external trigger of the waveform monitor as a reference signal to generate the trigger signal, and others to the channels of which waveforms are displayed in response to the trigger. This allows the phase differences between the television signals of the channel inputs relative to the reference signal to be measured. If the television signals of the channels are synchronized, the corresponding sync portions of the waveforms would align.
The waveform monitor may have a line select function that is useful to measure the phase relationship between the reference signal and other television signals of the channels. If a user selects the 102nd line, for example, this function would allow displaying the waveform of the 102nd line in the 1125 lines constituting one frame of the HDTV signal. If the reference signal is synchronized with the HDTV of the channel, the monitor would display a waveform overlapped by a picture signal wherein the overlap begins from the 41st line according to the HDTV standard, it being understood that line 41 is the first of the non-blanking lines. If they do not synchronize, the overlap would not begin from the 41st line but from another line.
If two television signals are of the same format, it is easy to generate the trigger signal according to the sync pulses because the intervals of the sync pulses are same. In case of different formats, such as HDTV and SDTV, it would be difficult to generate the trigger signal according to the horizontal sync pulses because the number of lines per field for the different formats, and hence the horizontal sync intervals, are different from each other.
As shown in FIG. 4A-4D, HDTV and SDTV signals having the same field interval (e.g. 16.68 ms, corresponding to a vertical frequency of 59.94 Hz) have different numbers of lines per field, for example, 562.5 and 262.5 lines respectively, in case of interlaced formats. Besides an SDTV (or HDTV) interlaced format has a different number of lines per field than an SDTV (or HDTV) non-interlaced format.
Video signals having the same content and field interval are sometimes delivered in different formats, that is, different definition levels and aspect ratios, such as HDTV and SDTV at present. So it is desired to measure the phase difference between one television signal as a reference signal and any of other different formats wherein the reference signal is provided to the external trigger terminal while the other signal is provided to the channel to display the waveform as to the horizontal sync signal. In one specific case of the above that is economical, an NTSC signal is selected as the reference, and the waveform of a selected line of an HDTV signal is displayed to measure the phase difference between them. This is because if a digital signal is selected as the reference, the decoder would currently be expensive.
As described above, what is desired is to display the waveform of a line of one television signal format though the reference signal for the trigger generation is in a different format having the same field interval but a different number of lines per field, such as the HDTV and the SDTV. It is also desired to provide a means for measuring the phase difference between the different television signal formats.